This invention relates to improvements in power-driven sheaves or blocks for hauling fish nets, such as purse seine nets, and is herein illustratively described by reference to the presently preferred embodiment thereof.
It has for some years been common practice to haul fishing nets draped over a power-driven sheave maintained in an elevated position over the deck of a fishing vessel, dock or barge. Suspended to swing and swivel from a boom or davit, the block addresses itself to the approaching and departing stretches of netting in accordance with the average of the force vectors created by tension in the two stretches of net. Despite this self-positioning action of the block tending to maintain the net centered in the sheave groove, there is a tendency for the cork line side of the net to be advanced faster than the lead line side, with attendant progressive skewing of the mesh out of square with the line of haul. There is a resultant tendency for the approaching netting with its associated lines and floats to pile up at one side of the sheave aggravating the differential. This tendency toward uneven hauling of netting may also be due in part either to directional constraints on the block or the netting, or to fold patterns in the approaching netting incidental to the hauling operation. Howeversuch unbalanced hauling and progressive skewing of the netting may occur, it tends to impair proper compaction and seating of the netting in the sheave groove necessary to gain maximum drive traction on the net and to minimize any tendency of netting to pile up and jam in the throat of the block. It also tends to make more difficult the removal of fish, seaweed and other objects, and to demand extra effort from the crew in straightening and squaring the net as it is being deposited on deck in preparation for subsequent resetting.
Because of these problems, experienced particularly in hauling large nets, block tilting mechanisms have been used heretofore which compensatively adjust the slope angle of the sheave axis of the block when the netting tends to pile up on one side or the other of the sheave during hauling operations. By raising the side of the sheave on which the pileup has occurred, the approaching netting tends to settle more compactly and centrally in the sheave groove as desired. Such prior mechanisms used a transversely arched hanger bar with a track spanning over the top of the block between the frame sides and carried by a track-engaging support trolley hung from the davit or boom. Cables passed from the davit or boom down through guides in the trolley extended to anchor points at the ends of the hanger bar. By drawing in one of the two cables while paying out the other, the trolley, hence the suspension point of the hauling block, was moved along the track to vary the tilt angle of the block.
It was found through experience, however, that hauling blocks rigged with such cable-type tilt mechanisms were bulky and there was a tendency at times for the cables to become fouled, causing undesired interruptions in the hauling and setting operations. Sometimes this occurred under sea and weather conditions making it dangerous, at least inconvenient, to correct the difficulty. A possibly more serious limitation of the cable controlled trolley arrangement was the difficulty at times in achieving precise and immediate control of block tilt. The lengthy tortuous runs of cables tended to develop slack, making use of the cables to position the trolley an exercise in successive approximations. Oftentimes under emergency conditions when accuracy and immediacy of control to change tilt of the block was essential, the cable system proved unsatisfactory. Further problems were experienced at times with edge portions of netting rolling up around the corks and sometimes around the lead line.
A broad object of the present invention is to provide an improved tiltable net hauling, power-driven block which avoids the above-mentioned difficulties and limitations.
A further object hereof is to provide a compact net hauling block having a remotely controlled tilt mechanism which adds no appreciable overall height or vertical length to the block and which is accommodated in the block structure without restricting space needed over the sheave to clear the netting passing through the sheave throat.
A further object is to provide an efficient and nonfouling tilt mechanism in such a hauling block so constructed as to function effectively in any of the varied marine environmental settings and operating conditions in which such hauling blocks are required to be used.
Still other objectives in such a net hauling block include: precision, directness and immediacy of control action of the tilt mechanism; a power-drive mechanism therein suitable for energization by means of hydraulic or electrical systems available on modern fishing vessels; and a tilt mechanism which is not adversely affected by wear over the useful operating life of a well-designed power block in which it may be incorporated.